This relates to imaging systems and, more particularly, to color correction in dual-band imaging systems.
Modern electronic devices such as cellular telephones, cameras, and computers often use digital image sensors. Imagers (i.e., image sensors) may be formed from a two-dimensional array of image sensing pixels. Each pixel receives incident photons (light) and converts the photons into electrical signals.
Typical imagers include red, green, and blue image sensing pixels and color correction circuitry. Red pixels may be configured to capture incident light in the red portion of the visible spectrum, blue pixels may be configured to capture incident light in the blue portion of the visible spectrum, and green pixels may be configured to capture incident light in the green portion of the visible spectrum. The color correction circuitry is used to correct the color balance of images captured by the imager using information on the relative intensities of incident light received by the red, green, and blue pixels.
Dual-band imagers used dual-band IR cut filter, which simultaneously pass photons in the visible spectrum and the near infrared (NIR) spectrum. At day time, both visible spectrum and near-infrared spectrum photons pass through dual-band IR filter. At night time, an additional near-infrared light source, which only emits NIR spectrum, is used to illuminant the scene, and the dual-band NIR image sensor perceives the NIR light signal. As an alternative, a mechanical switch could be used in a NIR imager to turn the IR-cut filter on and off as an alternative to a static dual band filter between day mode and night mode.
Dual-band IR imager has advantage of low cost and low maintenance compare to the mechanical IR filters switch approach. However, with dual-band IR imagers it is difficult to perform color reproduction for day mode because the visible light and NIR light are mixed, which violates the conventional principles of color reproduction. It would therefore be desirable to provide color correction circuitry and methods for dual-band imaging systems to handle the color reproduction difficulty.